Thermally-actuated electric switch



Feb. 20, 1923. 1,445,657 P. w. BAKER THERMALLY ACTUATED ELECTRIC SWITCH Filed NOV. 25, 1920 1}; vez; for.

Patented Feb. 20, 1923.

v OFFICE.

PERCY WILLIAM BAKER, OF LONDON, ENGLAND.

THERMALLY-ACTUATED ELECTRIC SWITCH.

- Application filed November 23, 1920. Serial No. 426,042.

To all whom it may concern:

Be it known that I, Pnnoy VVILLIAM BAKER, a citizen of the United Kingdom of Great Britain and Ireland, and resident of 72 Linzee Road, Hornsey, London, N. 8, England, have invented certain new and useful Improvements in a Thermally-Actuated Electric Switch, of which the following is a specification, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to an electric switch of the kind which is thermally actuated by current passing through it and in which a. base carrying suitable contacts, say spring contacts, is adapted to receive a movable or removable member, which I will call the carrier, upon which the thermally actuated device is mounted. The invention mainl comprises an improved form of tubular thermally actuated device and method of actuating and mounting the same.

According to my invention I proceed substantially as follows I arrange on the carrier :1. tube of metal, which is wound by a fine wire adapted when current is passing through it, to heat and expand the tube and by lengthening it to make a contact which will short circuit the wire winding and allow it to cool until the said tube contracts and breaks the circuit thus redirecting the current through the winding, re-expanding the tube which again contracts, the process being repeated as long as sufficient current is connected from the base contacts to the terminals, preferably knife terminals, onv the carrier. This fine wire is permanently connected. to the knife terminals and is short circuited only when the tube makes contact.

At one end of the carrier I lit a screw carrying a platinum or other suitable tip and immediately opposite I fit another tip to the end of the tube, which makes electrical and mechanical contact with the other blade or terminal.

The end of the tube next the tipped screw is normally out of contact and the other end of the tube ispreferably mounted on its blade terminal by slotting the tube and fitting it thereover.

The screw having the tip is preferably mounted within a screwed tube soldered or otherwise fixed to theterminal at that end. This tube may be twice slit or cut, one slit may be the full length of the screwed tube and the other say half the length. The strip of metal between the slits is bent inwardly so as to provide a firm but resilient grip on the screw.

The carrier is of non-conducting material and shaped so as to be easily taken in the fingers and thumb for removal and replacement.

The windings on the metal tube are suitably insulated from the tube as by wrapping the tube with paper or other material.

An example of the invention is shown in the accompanying drawings in whichjig. l is a view of the carrier in side elevation.

Fig. 2 and Fig. 3 shows the otherend.

Fig. 4 represents a suitable and known form of contact base.

Figs. 5 and 6 show details of the adjustable contact screw and its threaded and split holder.

Referring to Figs. 1 to (5 the carrier comprises a body part a of earthenware or like non-conducting material. On this body part two knife contacts .7) and c are mounted. The contact 0 supports the thermally-actuby a fine wire e is a View of one end of the carrier contact to the For the purpose of fixing the tube of on contact 0 the tube is split for say half an inch on opposite sides at m, w, to make a tight fit on the blade 0 and is then soldered, but other means of mounting and fixing may be employed. I 7

Within the body part of the other knife contact b a tl'ireaded tube is fixed and receives an adjustable screw 7 having a platinum or other suitable tip li positioned opposite a like tip i on the tube (1. A small gap is left be tween these tips when the tube is unexpanded but when expanded the contacts close together and a direct path from b to c or vice versa is established for the electric current.

The tube or holder 7 for the screw 9 is threaded and is slit at j, j and the smaller strip of metal is between the slits is bent slightly inwardly to provide a resilient grip for the screw.

The base shown in Fig. 4 comprises an insulating block Z and two spring clips m and n, with terminal screws. These receive the knife contacts I) and c.

Assume the carrier to be in position on the base and the current supplied thereto, the'preliminary flow will be from one contact to the other through the Wire winding 6, the heat of the wire will expand the tube d, tips h and i will close together and the current will pass from one contact to the other by way of the tube d.

The wire 6. will be short circuited and will cool, tube cl will contract, the tips h and i will separate and the current will then repass by the wire e, the tube will be reheated, the tips reclosed and the process repeated as long as currentflows thus producing an intermittent or flickering light in any lamps in the circuit. 7

What I claim and desire to secure by Letters Patent is 1. An electric SWltCl1,,C0l11PI'lSll1g a. body,

a pair of knife contacts, one secured to the body at each end thereof, a tube having one end slotted to receive one of the knife contacts and secured thereto and having a contact point on the other end, an adjustable contact point carried by the other knife contact-in alignment with the contact point on the tube, and a heating coil mounted on and insulated from the tube having electrical connection with both knife contacts for heating the tube, so that the same will expand to make electrical connection between the con tact points when connected in a circuit.

2. An electric switch, comprising a body, a pair of knife contacts, one secured to each end of said body, a tube having one end slotted to receive one knife contact and secured thereto and having a contact point on the other end thereof, a split sleeve mounted in the other knife contact and a contact member threaded in said sleeve having a point in alignment with said contact point on the tube, and a heating coil mounted on said tube, insulated therefrom and having electrical connection with both knife contacts, whereby the heating will cause the expansion of the tube in an electric circuit for closing the contact points to make a circuit thru the tube and vary the effect of the current in the circuit.

In witness whereof I have hereunto set my hand in presence of two witnesses.

PERCY WILLIAM BAKER.

Witnesses TRAYTON EDWARD BRADFORD, EDWARD GAMBLE \VARREN. 

